The effect of preheating on microhardness and flexural strength of Bulk-fill resin composites: An invitro study

Abstract

Introduction: Despite of the advantage of preheating for composites, the effect of this method on the physical and mechanical properties of bulk-fill resin composites has not been precisely defined. The aim of this present study was to evaluate the effect of preheating on the microhardness and flexural strength of bulk-fill resin composites. Methods and Materials: In this study, Xtra-fill and Opus composites were used to measure the microhardness and flexural strength. For each of the parameters, 42 speciments of each type of composites were prepared. 84 disk-shaped speciments of microhardness, 4mm in diameter and 2mm thick, and 84 bar-shaped speciments of flexural strength with a length of 25 mm and a square-section with dimentions of 2×2 mm were prepared as follows.Goup1:Xtra-fill composite with preheating(Composites are placed in a thermostatically controlled water bath at 68 degree of celcius for 15 minate.n=21) Group2:Xtra-fill composite without preheating(at room temperature.n=21) Group3:Opus composite with preheating(like group1.n=21) Group4:Opus composite without preheating(like group2.n=21). The microhardness of the samples will be checked with diamond-indenter vickers(Micro Vickers tester,Innovatest Micro Met II BUEHLER,IL,USA) of 50 gf for 15 seconds.Flexural strength will be done by ISO 4049 standard 3-point flexural test. Results: In the group with preheating, the average flexural strength in both Xtra fill and Opus composites was higher than the group without preheating (P – value<0/001). There was no significant difference in the mean microhardness between the two groups with preheating and without preheating in either type of composite (P - value = 0.719). The average flexural strength and microhardness of Xtra fill composite in both modes with and without preheating was higher than the average flexural strength of Opus composite( P-value<0/001). Conclusion: Finally, this study showed that preheatig bulk-fill composites up to 68 ° C have no negative effect on their microhardness and increase the flexural strength of these materials. In addition, the degree of microhardness and flexural strength of bulk-fill composites from different brands is not the same and depends on their chemical composition.